The invention relates to a method and a device for the path-dependent control of the force generated by a first piston, which piston travels in a first cylinder which is divided by the first piston into a first and a second chamber, a pressure fluid being introduced into the first chamber. A second cylinder is also provided for in which a second piston travels and is likewise divided by the second piston into a first and a second chamber.
A similarly designed system is known from DE-A-44 41 098 and functions as an actuation device boosted by external force. The fluid pressure is generated by a master cylinder and transmitted to the first chamber of a slave cylinder and the first chamber of the cylinder of a transmission unit. The system works hydraulically and the slave cylinder and the master cylinder of the transmission unit are stepped, the second chambers each having the greater diameter. As long as the external force exists, the transmission unit is held at rest position because the pressure generated by the master cylinder is not sufficient for moving the piston of the transmission unit against the pressure of the external force supply acting in the second chamber. When the external force supply is lacking, that counter force is absent and the piston is moved, whereby the second chamber is reduced. The pressure built up at the feed point of the external force is transmitted to the second chamber of the slave cylinder and thereby boosts it.
The objective of the invention is to control the force generated by a piston in the simplest possible manner with dependence on the path of travel of the piston.
This objective is achieved according to the invention by the two pistons being coupled so that the second piston is pulled along by the first piston, and by the second chamber of the first cylinder being connected to the first chamber of the second cylinder so that the same pressure prevails in both chambers.
When the first piston performs an extension movement, the fluid is conducted out of the second chamber of the first cylinder into the first chamber of the second cylinder. As the two pistons are coupled, they move synchronously so that in the event of an extension movement, the reduction of the second chamber of the first cylinder is accompanied by an enlargement of the first chamber of the second cylinder. If the diameter of the second cylinder is made greater than that of the first cylinder, the overall volume of the second chamber of the first cylinder and the first chamber of the second cylinder increases when the first piston performs an extension movement, so that the counterpressure falls and the force generated by the first cylinder increases continuously in a path-dependent manner when the first piston extends.
If, however, the second cylinder has a smaller diameter, the force generated by the first cylinder falls continuously when there is an extension movement.
In each case, the force generated by the first piston is a largely steady and linear function of its extension path.
The pressure in the second chamber of the second cylinder is preferably regulated so that it is always equal to the counterpressure, that is, the pressure in the first chamber of the second cylinder and in the second chamber of the first cylinder.
The two cylinder-piston units can be standard cylinders including a piston and the two chambers of each cylinder can have the same diameter. The coupling of the two pistons is appropriately mechanical and positive.
The initial value of the counterpressure of the first cylinder is preferably adjustable, to which end its second chamber can be connected to the source for pressure fluid, via a regulator at which the initial counterpressure value can be set.
The pressure fluid is preferably a compressed gas, especially compressed air. The source of the pressure fluid the pressure gas or the pressurized air is the sole power source of the system.
The invention can be used, for example, for a device for dispensing viscous compositions contained in aluminium cartridges having a corrugated surface. The viscous composition may, for example, be an adhesive. The cartridge is compressed for dispensing the compositions. The force required to do this increases according to the degree to which the cartridge is already compressed. Therefore, to dispense the viscous composition at a constant rate and volume, it is necessary to control the force exerted on the cartridge, and that being to have it increased, with dependence on the remaining size of the cartridge. To do this, the cartridge can be inserted into a dispensing device in which it can be acted upon by the first piston of the device according to the invention.